A ship lock, often in a canal system, operates to connect two bodies of water at different water levels by alternate lowering and raising of the water level in the ship lock. Ship locks are operated using the gravity force to transfer a volume of water from one side of a lock gate to its other side. Once water levels have equilibrated, the lock gate can be opened for the ship to move through the gate.
U.S. Pat. No. 4,310,769 issued Jan. 12, 1982 teaches a ship lock system having one or more underground hydroelectric pumped-storage units which generate electrical energy. Water from the ship lock is drained to a lower reservoir when the ship lock water level is lowered. The water passes through a penstock and past a pump-turbines to generate electrical energy. The reservoir collects the water instead of allowing the water to be lost downstream. The pump-turbines then pump the water from the reservoir upward into the ship lock through the penstocks to raise the water level in the ship lock. The electrical power for accomplishing the pumping action can be supplied from other conventional energy sources as well as from tidal, wind, solar and other emerging energy sources. Hence water is conserved by the use of the pump-turbine. While this operation conserves water, it is a net consumer of electricity as the electricity generated by lowering the water level in the ship lock will be less than the electricity needed to pump the water back up into the ship lock against the forces of gravity and other losses.
German patent application DE 11 30 766 published May 30, 1962, discloses a power station located next to a lock having a pump-turbine for enabling faster and cheaper operation of the lock where one of the generators of the power station can be used to speed up the lock operation.
However, neither of these two patents teach the net recuperation of the unused hydraulic energy to generate electricity. In a traditionally operated ship lock, once the operating valves are opened, the free discharge of water through the system is proportional to the square root of the differential head from the two sides of the lock gate. Thus, the discharge rate is usually high in the beginning, and then diminishes until the discharge rate becomes relatively small towards the end of the water transfer cycle making it difficult to recuperate hydraulic energy for generation of electricity. Hence there is a need to be able to have a net recuperation of unused hydraulic energy to generate electricity which takes into consideration the problems associated with changes in the discharge rate of the water flow.